Pacific North Equatorial Current bifurcation latitude and Kuroshio Current shifts since the Last Glacial Maximum inferred from a Sulu Sea thermocline reconstruction

The meridional migration of the bifurcation latitude of the Pacific North Equatorial Current (NEC) in the western boundary of the tropical Pacific modulates the strength of the Kuroshio Current. Using salinity reanalysis data, we show the NEC bifurcation latitude also acts as the dominant control on thermocline salinity of the Sulu Sea, just west of the Philippine archipelago, by regulating influx of western Pacific thermocline water via the Luzon Strait. We used oxygen isotopes (delta O-18) and Mg/Ca in the thermocline-dwelling foraminifera Globorotalia tumida from Sulu Sea sediment core MD97-2141 to determine past thermocline delta O-18(w) and salinity variability spanning similar to 20-5 ka with an average sampling interval of similar to 50 years and infer past changes in the NEC bifurcation latitude. Our Sulu Sea thermocline reconstruction reveals high salinity from similar to 18.8-15.5 ka, similar to 12.2-11.5 ka, and from similar to 9.5-8.5 ka indicating the NEC bifurcation latitude was shifted north and the Kuroshio was weak at those times. Low Sulu Sea thermocline salinity from similar to 13.0-12.4 ka, similar to 11.5-10.9 ka, and from similar to 8.5 ka until the end of the record at similar to 5.6 ka indicates the NEC bifurcation latitude was shifted south and the Kuroshio Current was relatively strong. Comparison to other paleoclimate records suggests the observed northward (southward) shifts of the NEC bifurcation latitude were driven by southward (northward) shifts of the Indo-Pacific ITCZ, consistent with modern mechanisms controlling interannual NEC bifurcation variability. The NEC bifurcation latitude shifts likely modulated northward energy transport via the Kuroshio Current and the mean temperature and salinity of the Indonesian Throughflow. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study shows that the meridional migration of the bifurcation latitude of the Pacific North Equatorial Current (NEC) influences the strength of the Kuroshio Current in the western tropical Pacific and controls the thermocline salinity of the Sulu Sea. By analyzing isotopic and elemental data from foraminifera in sediment cores from the Sulu Sea, past changes in thermocline salinity and NEC bifurcation latitude shifts have been identified over the last 20-5 thousand years.